Anatomy of Endovascular Arteriovenous Fistula Creation

Abstract

Endovascular creation of arteriovenous fistulas for hemodialysis access represents a promising alternative to surgical dialysis access provision. However, because the two available devices rely on the adequacy of the native vascular configuration, not all patients are candidates. Thus, a precise grasp of upper extremity vascular anatomy and the ability to apply that knowledge clinically are required. The purpose of this article is to provide an overview of endovascular arteriovenous creation, focusing on anatomic considerations, procedural steps, and outcomes.

The number of individuals with end-stage renal disease (ESRD) in the United States increased by 31% between 2002 and 2022, with the vast majority utilizing hemodialysis for renal replacement therapy. ¹ Although the Fistula First Breakthrough Initiative promoted by the National Kidney Foundation has been superseded by a more personalized approach termed the “end-stage kidney disease life-plan,” arteriovenous shunts (fistulas and grafts) remain the preferred form of access for most patients who require long-term hemodialysis. ² Compared with central venous catheters, shunts are associated with lower rates of infection and improved overall survival. ^{3 4} Between the two shunt types, fistulas have traditionally been reported to have fewer long-term vascular events than grafts, although some authors have called this into question. ^{2 5 6 7} Regardless, current consensus places fistulas as the first line among long-term hemodialysis access types. ⁸

Arteriovenous fistula creation has typically been performed surgically. Although a comparatively minor procedure, it is nonetheless associated with complications including bleeding and infection, and can be accompanied by significant surgical site scarring. Additionally, although the use of regional anesthesia is becoming more common, up to 85% of cases are still performed under general anesthesia, which carries with it substantial cost and patient risk. ⁹ Given that patients undergoing this procedure commonly have comorbidities that place them at elevated risk of adverse outcomes, the use of minimally invasive alternatives may be preferable.

Recently, two devices, the WavelinQ EndoAVF System (Becton, Dickinson, and Company, Franklin Lakes, NJ) and Ellipsys Vascular Access System (Medtronic, Dublin, Ireland), became available that allow for the creation of upper extremity endovascular arteriovenous fistulas (endoAVFs). Although preliminary evidence regarding their safety and efficacy is promising, these devices have relatively stringent anatomic requirements for use that preclude eligibility in some patients. Thus, candidate selection requires a precise grasp of upper extremity vascular anatomy and the ability to apply that knowledge clinically. The purpose of this article is to review endoAVF creation, focusing on anatomic considerations, procedural steps, and outcomes.

Anatomic Considerations

A detailed understanding of the upper extremity vasculature is essential to determining patient candidacy for endoAVF creation. Although the anatomy often appears straightforward based on the consistency with which it is presented in textbooks, the vascular pattern of the upper limb can be highly variable and thus particular attention must be paid to determine the best approach to access creation. ¹⁰

Arterial

As is typical throughout the body, upper extremity arterial anatomy is more consistent than is venous. The brachial artery represents the continuation of the axillary artery once it passes beyond the tendon of the teres major muscle. It gives rise to the profunda brachial artery in the upper arm as well as several collateralizing vessels around the elbow (radial and ulnar recurrent and collateral arteries) before dividing into the radial and ulnar arteries several centimeters distal to the elbow. ¹¹ The radial artery, the smaller but more direct continuation of the brachial artery, continues into the hand where it provides the dominant supply to the deep palmar arch. The larger ulnar artery gives rise to the common interosseous artery proximally, after which it continues into the hand to supply the superficial palmar arch. The common interosseous artery bifurcates into anterior and posterior interosseous branches, both of which taper above the wrist. The palmar arches anastomose in the palm, providing redundant supply to the structures of the hand and forearm. They can have a variety of configurations, but, in general, the deep palmar arch is complete in 95% of patients and the superficial arch in 80%. ^{12 13}

Deviation from conventional anatomy happens with some regularity. The most common variation is the presence of a brachioradial artery (also known as a high origin of the radial artery), which occurs in up to 14% of individuals. ^{10 14} In this variant, the radial artery originates somewhere between the axillary artery and elbow. Distal to this point, the parent artery is termed “the ulnar-interosseous trunk” and frequently forms an anastomotic arcade with the brachioradial artery in the upper third of the forearm. ¹⁵ Notably, a similar variant of the ulnar artery can also occur but is seen in less than 1% of patients. ^{10 12} Another frequent variant is the presence of a persistent median artery, which occurs in 4 to 12% of individuals. ^{10 12} This artery originates from the common interosseous artery and continues into the hand, to which it may provide the dominant supply. ¹³ A radial artery loop is observed in 1% of cases and, though not strictly a variant, can prove problematic when catheterizing the radial artery. ¹⁶ Many other variations have also been described but are much less commonly encountered and thus are beyond the scope of this review. ¹⁰

Venous

Venous anatomy is highly variable and differs from the arterial in that there are distinct deep and superficial systems. The veins of the former consist of small, paired venae comitantes (radial, ulnar, and brachial), while those of the latter represent the dominant outflow and largely lack direct arterial analogs. ¹⁵ The main veins of the superficial system are the basilic and cephalic, both of which originate from the dorsal venous arch/network of the hand. The basilic vein arises from the medial (ulnar) aspect of the arch and ascends along the dorsomedial aspect of the forearm before passing ventrally below the elbow. It crosses through the antecubital fossa and then continues up the arm medial to the biceps before piercing the deep fascia in the mid-arm to join with the smaller brachial veins. These vessels become the axillary vein at the lower border of the teres major. The cephalic vein arises from the lateral (radial) side of the arch. It wraps around the lateral border of the forearm to ascend on its ventrolateral aspect, passing through the antecubital fossa and continuing up the arm lateral to the biceps muscle. It perforates the clavipectoral fascia in the deltopectoral groove and ultimately drains into the axillary vein. An accessory cephalic vein is present in 36 to 75% of individuals; it ascends lateral to the cephalic vein and joins with it at the level of the antecubital fossa. ^{17 18}

The venous anastomoses in the antecubital fossa are essential to understand for the purposes of dialysis access creation, particularly those of the median antebrachial vein. This vein originates from the palmar venous plexus, ascends centrally in the ventral forearm, and drains into one or more vessels in the antecubital fossa. The venous anatomy in this region is particularly variable and has been classified into several types, the two most common of which are described here. ^{19 20 21} In one, termed the “N” or “H” configuration, a median cubital vein is present, which originates from the cephalic vein a few centimeters below the elbow, runs superomedially to drain into the basilic vein just above the elbow, and receives the medial antebrachial vein in its midportion ( Fig. 1a ). In the other, termed the “M” configuration, the median antebrachial vein bifurcates into median cephalic and median basilic veins that communicate with the cephalic and basilic veins, respectively; in this configuration, the median cubital vein is absent ( Fig. 1b ).

Fig. 1.

( a, b ) Diagrams of the two most common variants of forearm venous anatomy.

Perforator veins connect the deep and superficial veinous systems and are present throughout the arm; one, the perforator vein of the elbow, is essential for endoAVF creation. On the superficial side, this vessel connects with the medial antebrachial vein at its most cranial extent, either before the bifurcation into median cephalic and basilic veins or at the connection with the median cubital vein. ²² From this point, it passes caudal and posterior for a short course before draining into one of the adjacent deep veins. Because it is valveless, it allows flow in either direction as pressure differences allow.

Endovascular Fistula Creation

Endovascular fistula creation takes advantage of the natural geometry of the arm vasculature to create a side-to-side fistula. Because only the deep system has closely approximated arteries and veins, it is used for fistula placement. However, because those vessels are too small and deep to be used for dialysis access, the flow must be transmitted to the superficial system, which necessitates the presence of a patent perforator vein.

Preprocedural Evaluation

Because anyone healthy enough to undergo surgical arteriovenous fistula placement should be able to tolerate endoAVF creation, most limitations to candidacy arise not from comorbidities but from failure to meet the stringent anatomic criteria needed for utilization of these devices. Consequently, thorough preprocedural sonographic mapping is essential to determine whether endovascular fistula creation is feasible and, if so, which device to use.

WavelinQ

The WavelinQ system utilizes radiofrequency energy administered through magnetically aligned arterial and venous catheters to create an anastomosis between either the ulnar artery and vein or radial artery and vein. The following requirements must be met:

1. Adequate arterial inflow: brachial artery ≥ 2 mm.

2. Adequate venous outflow: basilic or cephalic vein ≥ 2.5 mm.

3. Absence of flow-limiting central stenosis.

4. Access vessels (brachial artery and brachial/radial/ulnar vein) ≥ 2 mm.

5. Perforator ≥ 2 mm in diameter and straight.

6. Artery and at least one of the paired veins at the target fistula site ≥ 2 mm.

7. Absence of excessive calcification at target fistula site.

Ellipsys

The Ellipsys system, by contrast, utilizes thermal energy to create an anastomosis between the proximal radial artery and perforator vein of the elbow. Unlike the WavelinQ system, the procedure can be completed under exclusively ultrasound guidance and requires only a single access. Anatomic requirements are as follows:

1. Adequate arterial inflow: proximal radial artery ≥ 2 mm.

2. Adequate venous outflow: basilic or cephalic vein ≥ 2.0 mm.

3. Perforator ≥ 2 mm in diameter and straight.

4. Distance between perforator vein and proximal radial artery < 1.5 mm.

5. Adequate palmar arch collateral circulation as evaluated by Barbeau or modified Allen's test.

6. Absence of excessive calcification at target fistula site.

Overall, 60 to 65% of patients are eligible for endoAVF creation using at least one system, with men and younger patients being more likely to meet anatomic requirements. ^{23 24} Candidacy rates appear largely comparable between the two systems, with patients meeting the criteria for WavelinQ in 30 to 54% of cases and for Ellipsys in 44 to 63%. ^{23 24 25 26 27} Comparison with rates of suitability for distal surgical AVF placement is challenging given the greater flexibility in available anatomic configurations; however, in the mentioned studies, suitability for placement of a distal fistula ranged between 32 and 51%. ^{25 26 27}

Procedure

EndoAVF creation is generally performed on an outpatient basis under moderate sedation with or without regional anesthesia. The patient is positioned supine with the arm hyperextended on an arm board, and the arm is prepped using standard sterile technique.

WavelinQ System

1. Access the brachial artery and perform an angiogram to confirm the target fistula location. Once it is decided to proceed, introduce a 5-Fr sheath over the wire.

2. Access either the brachial vein if using a parallel orientation or one of the paired radial/ulnar veins if taking an antiparallel approach and introduce a second 5-Fr sheath.

3. Advance the 4-Fr arterial catheter through the arterial sheath over the wire to the target fistula site under fluoroscopic guidance. Once in place, rotate it until the peaks of the backstop are oriented toward the target vein.

4. Introduce the 4-Fr venous catheter through the venous sheath over the wire into the vein under fluoroscopic guidance. Rotate it until the rotational indicators appear as open boxes and the arc of the electrode is pointed toward the artery.

5. Advance the venous catheter until the arc of the electrode sits within the concavity of the backstop on the arterial catheter and the electrode appears compressed.

6. Remove both guidewires and connect the venous catheter to the electrosurgical generator.

7. Under fluoroscopic visualization, press and hold the cut button, activating the electrode and creating the channel.

8. Remove the venous catheter followed by the arterial catheter.

9. Perform an angiogram to confirm fistula patency and absence of complications.

10. When more than one brachial vein is present and has significant outflow, it is recommended to embolize the dominant one to increase flow to the superficial vessels.

Ellipsys System ( Figs. 2 , 3 )

Fig. 2.

Series of ultrasound images illustrating the steps of endoAVF creation using the Ellipsys system. ( a ) A 21-gauge needle is navigated through the perforator lumen (arrows) until the tip enters the proximal radial artery (arrowheads). ( b ) A 0.018-inch wire (arrows) is introduced through the needle. ( c ) The needle is exchanged over the wire for a 6-Fr transradial sheath (arrows). ( d ) The Ellipsys device (arrows) is extended through the sheath in the open position (arrows). ( e ) The device is retracted until the distal footplate engages the wall of the radial artery (arrow). ( f ) The device is closed (arrow), compressing the walls of the proximal radial artery and perforator vein. ( g ) The device is activated as evidenced by the formation of echogenic material (arrow) at the fusion site. ( h ) The device is exchanged for a 5 × 20 mm semicompliant percutaneous angioplasty balloon, which is used to dilate the fistula at the anastomosis (arrows). ( i ) The anastomosis is maximally dilated when the balloon waist is fully effaced (arrows). ( j ) Doppler ultrasound of the fistula demonstrates low resistance waveforms and flow volumes measuring 610 mL/min within the brachial artery.

Fig. 3.

( a ) Anatomy of the endoAVF demonstrated on a fistulogram performed at the first maturation visit, during which the anastomosis was dilated to 6 mm. Flow volumes in the cephalic vein were measured at 1,500 mL/min. ( b ) Ellipsys anatomy brachial arteriogram via radial artery approach during first maturation visit, demonstrating a brachial arteriogram with patent anastomosis and perforator vein.

1. After placing a sterile tourniquet on the upper arm and while using ultrasound guidance, a needle is advanced from either the cephalic or the basilic vein, caudally through the perforator vein to the level of the closest point with the proximal radial artery.

2. The needle is then advanced across the soft tissues (should be less than 1.5 mm apart from one another) into the proximal radial artery under direct ultrasound visualization. The tourniquet is then removed and heparin can be administered once in the radial artery per physician preference.

3. A 0.018-inch wire is placed into the needle, which is exchanged for a 6-Fr thin-walled (transradial) sheath.

4. The 0.018-inch wire is replaced with a 0.014-inch guidewire, over which the Ellipsys catheter is advanced until the backstop of the catheter meets the sheath, effectively exposing the footplates of the Ellipsys device within the radial artery.

5. The device should be rotated so that the thumb tab faces the orientation with which the needle crossed into the artery (i.e., if the vein is at the 12 o'clock position to the artery, then the thumb tab should be pointed to the 12 o'clock position). The device is then retracted until the distal (caudal) footplate of the device engages the proximal radial arterial wall, as confirmed by a gentle tugging motion confirming capture.

6. The device is closed by retracting the thumb tab on the handle, thereby engaging and capturing the proximal radial artery and perforator vein. A measurement of less than 0.7 mm should register on the power controller that is attached to the device.

7. The device is then activated, and through a series of pulse cycles, the footplates of the device will fuse the radial artery to the posterior wall of the perforator vein.

8. After completion of the heat cycles, the device is removed with gentle traction. If the device is adherent to the fused tissue, the “release cycle” option can be used for additional heat pulses, which will free the tissue from the device.

9. The device is then exchanged for a 5 × 20 mm semicompliant balloon, which is inflated to effacement. It is practitioner dependent on how long this balloon can stay inflated but typically between 30 and 120 seconds.

10. The balloon is then removed, and completion ultrasound should be performed of the brachial artery to obtain brachial artery waveforms and flow volumes. Ideally, this shows a low resistance waveform with flow volumes greater than 250 mL/min.

Conclusion

As minimally invasive options continue to replace surgical approaches and direct visualization is replaced by indirect imaging, an understanding of standard anatomy as well as common deviations from it will be increasingly necessary. The development of endoAVFs leveraged such knowledge for the development of the procedure and remains essential for patient selection. Ideally with time, new approaches will broaden patient eligibility and new procedures, both dialysis-related and otherwise, can be developed.